Pamestique 

Upgrades: if weight is your issue...lose 5 lbs. Makes no sense to pay good money for lighter components when you weigh too much to begin with...

If you are looking for performance and durability... now that can be helped. Again I already said higher end components perform better. In order to check it out go to the bike shop and test ride a bike with Ultegra or Dura Ace shifters. Not certain I would worry about upgrading from Tiagra to 105 but at some point you might want to go up to Ultegra. Clean smooth shifting adds in performance on the bike.

I also believe in a good custom set of wheels. I can't tell you how much difference it feels than stock wheels. See if you can find a bike shop that will loan you some good wheels. You have to check it out to see the difference.

I went from a 20 year old Specialized Expedition to a Lemond Zurich with full Ultegra. I immediately felt the difference. The bike was lighter, more responsive, shifted beautifully, went faster and I could ride harder and farther. It made me wnat to ride more. My new bike is so much more than that. Recently I purchased a new mountain bike. I have already switched out the crank, wheels, brakes and fork. Bike performed well before but now so much better.

But I have a friend who rides old cheap bikes. I can't even come close to her performance (when she ride with me its a "social" ride for her). She blows me away... that because her engine is as fit as it comes and good or bad bike, she can ride. People like me need some help but frankly, if I lost 10 lbs I probably would not need the Sram XX 36t in rear. But I will keep it because of the "bling" factor which after all is important as well.